Switched reluctance machines are often used as a generator to convert mechanical power received from a primary power source, such as a combustion engine, into electrical power for powering one or more loads of a work machine, or as a motor to convert electrical power within a common bus or energy storage device into mechanical power, such as rotational power for driving wheels, tracks or other traction devices. Switched reluctance motors may also be used as a generator to convert mechanical power received through traction devices, such as during regenerative braking, into electrical power for storage or for use by other loads. Among alternative electric machines, switched reluctance machines have received increased interest for being robust, cost-effective, and generally more efficient. As technology advances, so does the desire to operate switched reluctance machines more efficiently and reliably.
In a typical single-stage or single-machine application, a converter circuit having a series of conductors and switches, such as insulated gate bipolar transistors (IGBTs), is used to engage the individual phases of the connected switched reluctance machine in a manner which either generates electrical energy via the stator thereof, or generates mechanical or rotational energy via the rotor thereof. Multi-stage or multi-machine applications may also be used such as for applications involving higher power or higher load demands. In a multi-stage application, a series of switched reluctance machines can be simultaneously employed by a work machine as generator or motors. However, a multi-stage application would also require as many converter circuits, and even more capacitors and switches, as there are switched reluctance machines. As the number of electrical components increase, the challenges to implementation also increase. Moreover, although conventional power electronics configurations may be adequate for some large scale applications, the scalability of conventional configurations is still limited by physical and performance constraints.
Conventional power modules for multi-stage applications may have one or more capacitors, switches disposed on a heat sink, a bus bar coupling the switches to the capacitors, and a housing encasing the power module. This prior art configuration of a power module can be implemented for use with small scale two-stage systems, large scale two-stage systems, and larger scale three-stage systems. Notably, prior art power modules are designed to use only a single side or surface of the given heat sink. This one-sided configuration causes the size, or at least the length, of the conventional power module to sharply increase for each converter circuit, stage or switched reluctance machine that is added to the system, and thereby makes actual implementation more challenging for larger scale systems due to space limitations.
In addition, conventional power modules may be more susceptible to failures common to the power electronics for switched reluctance machines. In particular, the typical square wave switching patterns applied to the transistors or switches in the power module may cause high rise rates in current. The high rise rate in current, when coupled with the high inductance path typically found in conventional power modules may further cause large voltage overshoot conditions that can damage the transistors or switches. The one-sided or asymmetric nature of conventional power modules, or the uneven and relatively lengthy paths between the capacitors and the switches, also create more unwanted inductance which can expose the switches to more wear and premature failures.
Some converter circuit arrangements may be more compact in design, but are still susceptible to failures due to asymmetric designs. One such configuration is provided, for example, in U.S. Pat. No. 7,327,024 (“Stevanovic”), which employs both layers of a substrate heat sink to take up less space. However, because the capacitors in Stevanovic are not included in the power modules, but rather along the receptacles which receive the power modules, the configurations in Stevanovic are limited in terms of scalability. Furthermore, due to the geometry of the receptacles in Stevanovic, the distances or inductance paths between the capacitors and switches thereof are not substantially reduced or equidistant. Still further, the switches in Stevanovic are also not symmetrically distributed within each power module, but rather alternates with the positions of the diodes on each substrate layer. The alternating switches in Stevanovic, in combination other asymmetries, may introduce unwanted inductance.
In view of the foregoing disadvantages associated with conventional power modules and electronics for large scale electric drive systems, a need therefore exists for more compact, cost-effective and scalable solutions which reduce parasitic inductance and promote the reliability of switches. Accordingly, the present disclosure is directed at addressing one or more of the deficiencies and disadvantages set forth above. However, it should be appreciated that the solution of any particular problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent expressly noted.